How to Identify Overlapping Date Ranges in PostgreSQL for Player Team Membership?

Identifying Overlapping Date Ranges in PostgreSQL

Problem

A user seeks to retrieve a list of players who belonged to a specific team within a given year range. The initially proposed query is as follows:

SELECT * 
FROM   contract 
JOIN   team USING (name_team) 
JOIN   player USING(name_player) 
WHERE  name_team = ? 
AND    DATE_PART('YEAR',date_join)>= ? 
AND    DATE_PART('YEAR',date_leave)<p>However, this query does not effectively identify overlapping date ranges.</p><p><strong>Correct Solution</strong></p><p>To accurately determine overlapping date ranges, the query must be modified to consider the following criteria:</p><ol>
<li>Players who joined the team before the start of the specified year range.</li>
<li>Players who did not leave the team before the end of the specified year range.</li>
<li>Players who never left the team (represented by NULL date_leave values).</li>
</ol><p><strong>Optimized Query</strong></p><p>The following query provides a more accurate solution:</p><pre class="brush:php;toolbar:false">SELECT DISTINCT name_player 
FROM   contract
WHERE  name_team = ? 
AND    (date_join, COALESCE(date_leave, CURRENT_DATE)) OVERLAPS
       (date '2009-01-01', date '2010-01-01');  -- upper bound excluded

Explanation

• The COALESCE function is used to handle NULL date_leave values, considering them as open ranges.
• The OVERLAPS operator automatically sets the start of each interval as the earlier value of the pair.
• The daterange '[2009-01-01,2010-01-01)' represents a half-open interval, excluding the upper bound.

Additional Considerations

• In PostgreSQL 9.2 or later, range types can be used with index support, providing improved performance for range-based queries.
• The provided query can be further optimized by creating an expression index on the daterange(date_join, date_leave) expression.

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